The solubility of a metal sulphide depends upon pH of the solution. If true write 1, else write 0.
1. TrueSulfide solubilities vary over an exceptionally wide range of
values. Advantage is taken of this in the standard scheme for the qualitative
analysis of salts. The more insoluble sulfides (Group II, including both
ZnS and FeS) are first precipitated by adding H2S to the acidic
solution remaining from the precipitation of the Group I chlorides.
Subsequent addition of NaOH then brings down the more soluble sulfides of
Group III, as well as the hydroxides of Cr and Al.
This separation is based on the way in which pH controls the
concentration of S2– in
the solution. At pH values of around 7 or below, the concentration of S2– was said to be so small that only the
most sparingly soluble sulfides would precipitate. As the pH is raised to 12 or
so, the S2– concentration
would rise enough to precipitate the less-insoluble sulfides.
Sulfide solubilities vary over an exceptionally wide range of values. Advantage is taken of this in the standard scheme for the qualitative analysis of salts. The more insoluble sulfides (Group II, including both ZnS and FeS) are first precipitated by adding H2S to the acidic solution remaining from the precipitation of the Group I chlorides. Subsequent addition of NaOH then brings down the more soluble sulfides of Group III, as well as the hydroxides of Cr and Al.
This separation is based on the way in which pH controls the concentration of S2– in the solution. At pH values of around 7 or below, the concentration of S2– was said to be so small that only the most sparingly soluble sulfides would precipitate. As the pH is raised to 12 or so, the S2– concentration would rise enough to precipitate the less-insoluble sulfides.
